Audion amplifier



Dec. 12, 1933. DRAKE 1,938,656

AUDION AMPLIFIER Filed Feb. 6, 1931 2 Sheets-Sheet 1 Dec. 12, 1933. F, H. DRAKE AUDION AMPLIFIER Filed Feb. 6. 1931 2 Sheets-Sheet 2 9 iflm i I /4 Patented Dec. 12, 1933 PATENT" OFFICE I AUDION AMPLIFIER Frederick H. Drake, Boonton, N. J., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y.,'a corporation of Delaware Application February 6,1931. Serial No. 513,993

6 Claims.

This invention relates to audion amplifiers, and Y more particularly to amplifiers which include intersta ge coupling impedances designed for ready removal, and replacement by similar impedances ofdifferent magnitude, to permit operation over different frequency bands.

' One conventional method employed in adapting a radio receiver for use at different frequency bandsinvolves the substitution ofcoil assemblies 10 which form part'of the interstage couplings in a tuned radio frequency amplifier. sensitivity is desired, there maybe several tuned stages,- thus increasing. the number of interchangeable parts which must be kept at hand, and increasing the time and work required to shift fronrone frequency range to another. Furthermore, this increase in the number of parts which must be changed raises a possibility that the amplifier maybe rendered substantially inoperative by failure to make appropriatechanges in all of a the removable circuit elements. The desirability of a simpler system ingthe frequency range in radio receivers has been recognized but previous attemptstoavoid the changing ofa number of separate units have been unsatisfactory. Inparticular, it has been considered impractical to construct all of the re- I placeable'elements of one frequency range as a single assembly which couldbe connected to or 30, removed from the receiver chassis as a single unit. With one particular receiver in which the radio frequency'transformers were mounted within individual shields or coil cans, the receiver operation was unstable when all of the coil cans were secured to a plate to constitute a mngle unit.

Froma theoretical consideration of theprob- 1 lem, it was assumed that some new electrical couplings were established by mounting the coil cans upon'asingle supporting plate, since this step 40,;a'ltered the operation of the receiver. According to theknown design practice, it was believed that such incidental couplings could be avoided by grounding all of the coil cans upon each other, either through the supporting plate itself, or by additional low resistance connections. In actual practice, however, the operating characteristics of the amplifier were still affected even though the coil cans were carefully grounded-to their supporting plate, and attempts to construct unit or gang coil assemblies were abandoned under the belief that the mechanicalinterconnection of the separate units resulted in unstable operation even though no new electrical couplings were established by the mechanical coupling of the units in, .a single assembly.

When high for chang-s t be apparent from the following specification,

According to theypresent invention, stable operation is obtained, while employing ganged A,

.0011 or transformer elements by so constructingthe assembly that the mechanical interconnection of the parts does not give rise to the establishment of electrical couplings between the coils or transformers. I havefound that the mechani-' cal interconnection of a plurality of coil cans, each individually grounded upon the amplifier chassis, will not affect the electrical operation of the,

amplifier when care is taken to avoid the ground ing of the coil cans upon the connecting or supporting plate.

An object of the invention is to provide s. mul-- ti-sta'getuned amplifier of the type-having interstage coupling impedances which areremovable as a single unit, and in which the performance of the amplifier-is substantially unaffected by the mechanical interconnection ofthe cou. pling impedances. A further object is to provide an amplifier of the type stated, in which the coupling impedances arecoils mounted with- I, in shielding cans, and the mechanical assembly of the coils is effected by securing the cans to,; but insulating thesame from, a metal plate. Further specific objects relate to the provisionof novel forms of shielding cans, and assemblies of.-

shielding cans. a These and other objects of the invention .willwhen takcnowith the accompanying drawings,

in which, I V r Fig. 1 is aside view,with parts broken'away, of a radio receiver, g V q Fig. 2.18.311 enlarged plan view of a coil formand the shield'cap upon which it is mounted, a diagramof associated circuit elements being su- I perposed upon theview of the coil form,- Fig. 3 is'an enlarged fragmentary view, in perspective, of the top of one of the coil assembly shields,

Figs. 4 and 5 are an inside plan and an elevation, respectively, of the removable coil assembly, and

Fig. 6 is an enlarged section of a portion of the.

coil assembly.

.In the drawings; the reference numeral 1 identifiesthe outer casing of a radio receiver which'includes a plurality ofstages of tuned radio frequency amplification, the particular receiver illustrated in Fig. 1, being ofthe typedescribed' and claimed in the copending applica-. ti'on of.John E. Johanson, Ser. No. 513,999 filed February 6, 1931. Asdescribedin the .Jo'hanson application, one wall of the receiver casing is proto the space to be occupied by induotances or transformers which, with the several sections of a gang condenser 3, provide the tuned interstage couplings of the'radio frequency stages. A plate 4 of insulating material carries groups of expansible or' frictional terminals 5' which engage socket terminals on the removable coil elements to effect the desired electrical connections when the coils are assembled on the receiver chassis, one such group of terminals being shown at the left side of Fig. l. The opening 2 in the wall of the receiver is closed byv a metal cover plate 6 which has a handle '7, for convenience of manipulation, and is provided with sliding latches: 8 that engage pins 9 to secure the cover to the receiver casing.

The general construction of the interchangeable coils and their, shielding cans may follow the usual design practice. As illustrated, a coil form 16 of insulating material is secured to ametal cap or base 11 by a plurality of studs 12 which are fixed in the coil base '13 and, riveted to the cap 11. As shown diagrammatically in Fig. 2; the electrical structure of the interchangeable unit may be that of a transformer, having a primary P and secondary S, which is wound upon the cylindrical portion 10 of the coil form.

The respective windings are connected between tubular or socket terminals .14 that extend through the base 13 of the coil form. When the coil unit is plugged into the receiver, by fitting the socket terminals 14 over the pin terminals 5 of the receiver, circuitconnections as illustrated in Fig; 2 are established, i. e., the primary winding P is connected between the plate of the amplifier tube 15 anda lead 16 which extends to the source of-plate current supply, the lead being by-passed for radio frequencies by a condenser 17. The secondarywinding Sis connected between ground and the control grid of the succeeding tube 18, which may be another amplifying tube or the detector. The condenser unit 3 is permanently connected between the control grid and the ground, i. e., a point on the chassis of the receiver, and constitutes'the adjustable tuning element of the interstage couplingj One of the studs 12 is connected, by a jumper 19, to the grounded terminal 14 of the secondary S, thus grounding the shield cap 11 upon the chassis.

The shielding o'fthe individual-coil elements is completed by the cylindrical boxesor coil cans 20' which fit within and are secured to the caps 11. As best shown in Fig. 3, a plurality of internally threaded rivets 21 are secured to the ends of the coil cans, the heads of the rivets being ly greater thickness than the end wall of the cell can, thus facilitating the fitting of the groups'of coil terminals 14 upon the stationary pin terminals 5 by permitting the individual coll" cans to havea-slight tilting movement with respect to the cover plate 6. .Thecap 11 is provided with apertures 26 which are of appreciably larger diameter than the pin terminals 4., thus preventing inadvertent shorting of the tube circuits when the coil assembly isapplied to or removed from the receiver without f rst opening the supply cir-,

cuits.

While the invention has been described in connection with a radio receiver of the tuned radio frequency amplification type, it will be apparcut that it is not limited in its application to any one type of amplifier. The same principles apply equally well in the construction of other tuned or untuned amplifiers which are adapted for operation over different frequency ranges by removable interstage coupling impedances. V I claim:

1. A multi-stage amplifier of the type including a plurality of individually shielded removable interstage coupling elements, each coupling element with its respective shield forming an integral unit, and means mechanically intercom nesting all of said shielded elements to permit the simultaneous removal of all of said coupling elements from the amplifier, said means including insulating material preventing current flow from one coupling element to another along said mechanical interconnecting means.- l

2. In a multi-stage amplifier, a removable. interstage coupling system comprising a coil element for each stage of said amplifier, a metallic coil can supporting and shieldingeach of said cell elements, terminalsior each coil element en aging relatively stationary terminals of said amplifier, and means mechanically securing all of said coil cans to-a plate, said means including insulation preventing current flow from one can 'toxanothe'r along said plate.

and supporting each or" said forms, coil terminals carried by each of said forms for cooperation with the respective groups of fixed terminals, and means mechanically, connecting said metallic shields to permit the simultaneous engagement of all of said cooperating groups of terminals, said means comprising non-conducting material insulatingisaid shields from each other. I

4.. In a radio receiver, the combination with a casing having an-opening in one wall, of 'aclosure for said opening, a plurality of coupling coil shields and means for mounting the shields on said closure, each of said .rneansincluding a pair of insulating plates disposed on opposite 7 sides of one end wall of each of said shields, a

rivet extending through said plates and insulated from said shields whereby said shields are insulated from one another.

5. A removable coil assembly for a multi-stagc amplifier comprising a plurality of coil units, a shield can for each coil unit, each'of said coils with its respective shield forming an integral unit, a supporting plate, and means supporting all of said shield cans on said plate'and insulating said cans from each other a 6. The invention as set forth claim'g-S, where in said plate is metallic; and said supporting to the respective cans, and screws threaded into said rivets to secure the cans to said plate.

FREDERICIQ H. DRAKE. 

